Our objective is to determine the mechanism(s) by which prolactin (PRL) stimulates lactational processes and cell proliferation in the mammary gland. We and others have recently shown that: a) PRL alters the fluidity of plasma membranes, b) phospholipases A2 and C will duplicate certain of the actions of PRL in cultured mammary tissues, c) PRL stimulates cell division in a lymphoma cell line, d) the actions of PRL require ongoing polyamine synthesis, and e) the PRL stimulation of fatty acid synthesis entails and 6-8 hour delayed-response. Studies of the mechanism of PRL action are important because: a) they will help us understand how PRL regulates lactogenic processes, b) they can help us understand how PRL regulates proliferative processes in normal and neoplastic cells, and c) such investigations can serve as a model for understanding how hormones in general have effects on differentiative and proliferative processes in target cells. Our specific aims are as follows: a) to determine if the primary action of PRL on lactogenic processes in cultured mammary cells is associated with perturbations in phospholipid metabolism; specifically we will focus on the possible action of PRL on a phosphatidylinositol-specific phospholipase C, b) to determine if perturbations in phospholipid metabolism (as in a) are involved in the primary action of PRL on mitogenic processes in a PRL-responsive lymphoma cell line, c) to determine how PRL regulates polyamine metabolism by determining if and how PRL regulates the enzymes S-adenosylmethionine decarboxylase and spermidine synthase, and d) to determine how PRL has its early action on free fatty acid synthesis by determining if and how PRL stimulates the enzymes acetyl CoA carboxylase and/or fatty acid synthase.